Photoelectric conversion apparatus

ABSTRACT

A photoelectric conversion apparatus has: a plurality of pixels having mutually different color filters, and generating pixel signals by a photoelectric conversion; a color selecting switch for selecting the pixel signals generated by the plurality of pixels having mutually different color filters; a first amplifier circuit for amplifying at mutually different gains the pixel signals generated by the pixels having mutually different color filters and selected by the color selecting switch; a reference voltage connecting switch for selecting a reference voltage; and a second amplifier circuit for amplifying at mutually different gains the reference voltages correspondingly to the pixel signals of mutually different colors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoelectric conversion apparatuswhich is used in a scanner, a video camera, a digital camera, or thelike.

2. Description of the Related Art

In recent years, there is such a tendency that a high speed is requiredin a photoelectric conversion apparatus. The method disclosed in theOfficial Gazette of Japanese Patent Application Laid-Open No.2010-199710 (Patent Literature 1) is mentioned as one of units forrealizing the high speed. According to Patent Literature 1, by usingsuch a circuit construction that pixel signals of the same color areread out in parallel from a plurality of common output lines and colorsignals of a plurality of colors are read out from each common outputline for one horizontal scanning period, a light weight of common outputline capacitors is realized, thereby improving speed performance.

According to Patent Literature 1, a point that an amplifier unit isprovided for each pixel column and a gain (amplification factor) of theamplifier unit can be switched in accordance with the color has beenmentioned. If the gain differs in dependence on the color, noises due toa color selecting switch such as charge injection, clock feed through,or the like are generated, and a difference occurs between levels of thenoise contained in the color signals. Thus, when a dark signal is readout, a step shaped signal level difference occurs between the colorsignals and appears as a stairway-shaped waveform when seen for thewhole one horizontal scanning period. Such a distortion of the waveformbecomes a factor which causes DSNU (Dark-Signal-Non-Uniformity) todeteriorate.

The invention is made in consideration of the foregoing problems and itis an aspect of the invention to provide a photoelectric conversionapparatus in which the DSNU is small.

SUMMARY OF THE INVENTION

According to an aspect of the invention, a photoelectric conversionapparatus comprises: a plurality of pixels having mutually differentcolor filters, and generating pixel signals by a photoelectricconversion; a color selecting switch configured to select the pixelsignals generated by the plurality of pixels having mutually differentcolor filters; a first amplifier circuit configured to amplify atmutually different gains the pixel signals generated by the pixelshaving mutually different color filters and selected by the colorselecting switch; a reference voltage connecting switch configured toselect a reference voltage; and a second amplifier circuit configured toamplify at mutually different gains the reference voltagescorrespondingly to the pixel signals of mutually different colors.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a construction of aphotoelectric conversion apparatus according to the first embodiment ofthe invention.

FIG. 2 is a timing chart illustrating an example of processes of thephotoelectric conversion apparatus of FIG. 1.

FIG. 3 is a diagram illustrating an example of a construction of adifference detection unit.

FIG. 4 is a diagram illustrating an example of a construction of thedifference detection unit.

FIG. 5 is a diagram illustrating an example of a construction of aphotoelectric conversion apparatus according to the second embodiment ofthe invention.

FIG. 6 is a timing chart illustrating an example of processes of thephotoelectric conversion apparatus of FIG. 5.

FIG. 7 is a diagram illustrating an example of a construction of apixel.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

FIG. 1 is a diagram illustrating an example of a construction of aphotoelectric conversion apparatus according to the first embodiment ofthe invention. A plurality of pixels 100, 110, and 120 indicate an Rpixel, a G pixel, and a B pixel which have different color filters ofred (R), green (G), and blue (B) and generate pixel signals by aphotoelectric conversion. Each of the R pixel 100, G pixel 110, and Bpixel 120 is constructed by a circuit as illustrated in FIG. 7. In FIG.7, a photodiode PD converts light into electric charges by aphotoelectric conversion and accumulates them. By applying a reset pulsepres to a gate of a resetting transistor M1, the resetting operation ofthe photodiodes PD and floating diffusion FDs in the pixels 100, 110,and 120 is controlled. By applying a transfer pulse ptx to a gate of atransfer transistor M2, the transfer operation of the charges from thephotodiodes PD to the floating diffusion FDs is controlled. The floatingdiffusion FD accumulates the charges. An amplifying transistor M3 is aninput unit of a source follower circuit which is made operative by acurrent source iref for outputting an output according to an electricpotential of the floating diffusion FD from a terminal out to circuitsat the post stage.

A color selecting switch group 200 is provided. Color selecting switches201, 202, and 203 are provided to select the pixel signals of thedifferent colors of the R pixel 100, G pixel 110, and B pixel 120,respectively. The color selecting switches 201 to 203 are controlled bycontrol signals psw_r, psw_g, and psw_b, read out the color signals fromthe pixels 100, 110, and 120, and output to circuits at the post stage,respectively. A reference voltage connecting switch 230 has the samecircuit construction as that of each of the color selecting switches201, 202, and 203 and is provided to select a reference voltage Vref. Itis desirable that the reference voltage Vref is set to almost the samevoltage value as that of an output voltage at the time of shielding thepixels 100, 110, and 120 against the light.

A color signal input capacitor group 300 is provided. Color signal inputcapacitors 301, 302, and 303 are provided to sample the color signalswhich were read out by the color selecting switches 201, 202, and 203,respectively. A reference voltage input capacitor 310 is provided tosample the reference voltage Vref which was read out by the referencevoltage connecting switch 230. It is assumed hereinbelow that the colorsignal input capacitor 301 is set to Cr, the color signal inputcapacitor 302 is set to Cg, the color signal input capacitor 303 is setto Cb, and the reference voltage input capacitor 310 is set to Cref,respectively. It is also assumed that capacitance values of Cr, Cg, Cb,and Cref are equal.

In each of column amplifier circuits 400 and 410 of a switched capacitoramplifier type, the color signal input capacitor group 300 and thereference voltage input capacitor 310 are used as input capacitors. Thecolumn amplifier circuit 400 is a first amplifier circuit foramplifying, at different gains, the pixel signals of the color filtersselected by the color selecting switches 201 to 203. The columnamplifier circuit 410 is a second amplifier circuit for amplifying thereference voltage Vref selected by the reference voltage connectingswitch 230 at a different gain of every color filter. Amplifiers 402 and412 are provided. Feedback capacitors (403 and 404) and (413 and 414)are provided to decide the gains (amplification factors) of the columnamplifier circuits 400 and 410 on the basis of ratios between theircapacitance values and Cr, Cg, Cb, or Cref, respectively. It is nowassumed that the capacitors 403 and 413 are the first feedbackcapacitors (hereinbelow, referred to as Cf1, Cf1′), the capacitors 404and 414 are the second feedback capacitors (hereinbelow, referred to asCf2, Cf2′), and the capacitance values of Cf1 and Cf1′ are larger thanthose of Cf2 and Cf2′ (that is, Cf1>Cf2; Cf1′>Cf2′). Gain controlswitches (405 and 406) and (415 and 416) are controlled by controlsignals pgain<0> and pgain<1> and switch the gains by changing totalcapacitance values of the feedback capacitors of the column amplifiercircuits 400 and 410, respectively. A resetting switch 401 is providedto reset signal components accumulated in the capacitor Cf1 or Cf2 bysetting a control signal pc0 r to the high level and short-circuitingboth terminals of the capacitor Cf1 or Cf2. A resetting switch 411 isalso provided to reset signal components accumulated in the capacitorCf1′ or Cf2′ in a manner similar to that mentioned above.

Horizontal read out switches 503 and 513 are controlled by horizontalscanning pulses phs<0> and phs<1> and are provided to read out outputsignals of the column amplifier circuits 400 and 410 and output tocircuits at the post stage. The horizontal read out switches 503 and 513are switches for time-divisionally reading out the pixel signalsamplified by the column amplifier circuit 400 and the reference voltageamplified by the column amplifier circuit 410 and outputting to a samehorizontal common output line 701. The horizontal common output line 701is provided to transmit the signals read out by the horizontal read outswitches 503 and 513 to circuits at the post stage. A differencedetector 600 uses the horizontal common output line 701 as an input anddetects a difference between the signal based on the reference voltageVref and the color signal. The difference detector 600 executes adifference process for obtaining a difference between the pixel signalsamplified by the column amplifier circuit 400 and the reference voltageamplified by the column amplifier circuit 410. FIG. 3 illustrates anexample of a circuit construction of the difference detector 600. Aclamping capacitor 610 is provided to execute a clamping process by aclamping switch 620, a clamp voltage VCLAMP, and a control pulse Φ1. Anexternal output control switch 640 is controlled by a control pulse Φ2and is provided to control timing for outputting the clamped signal tothe outside. A buffer circuit 650 is provided to output the signalclamped by the clamping capacitor 610 to the outside.

Although the embodiment has been described with respect to theconstruction on the assumption that the pixels of each of the colorpixels 100, 110, and 120 of R, G, and B is constructed by one pixel forsimplicity of explanation, actually, a plurality of pixels are formed ina line with respect to each color. A common amplifier unit and a commonoutput signal line are provided for the different color signals of therespective colors in the sub scanning direction and the color signalsare line-sequentially output.

FIG. 2 is a timing chart illustrating an example of processes of thephotoelectric conversion apparatus of FIG. 1. The circuit operation inFIG. 1 will be described hereinbelow with reference to FIG. 2. For aperiod of time from time t0 to t1, the reset signal pres is set to thehigh level, the resetting transistor M1 is turned on, and the floatingdiffusion FD is reset to a power voltage. Each of the R pixel 100, Gpixel 110, and B pixel 120 outputs the reset signal. Subsequently, thecontrol signals psw_r, psw_g, and psw_b are sequentially set to the highlevel, the color selecting switches 201 to 203 are sequentially turnedon, and the reset signal to the color signal input capacitor group 300is clamped. At the same time, a resetting process of the columnamplifier circuits 400 and 410 is executed by the control signals pc0 r,pgain<0>, and pgain<1>. At this time, a control signal psw_ref is set tothe high level, the reference voltage connecting switch 230 is turnedon, and the reference voltage Vref to the reference voltage inputcapacitor 310 is also clamped.

After time t1, the transfer pulse ptx is set to the high level, thetransfer transistor M2 is turned on, and the charges are transferredfrom the photodiode PD to the floating diffusion FD. Thus, the colorsignals according to the charge accumulation time and the incident lightare output from the color pixels 100, 110, and 120. For a period of timefrom time t1 to t2, since the control signal psw_r is set to the highlevel, the color selecting switch 201 is turned on, and the color signalwhich is output from the R pixel 100 is input to the color signal inputcapacitor 301. A difference between the reset signal of the R pixel 100and the color signal is amplified by the column amplifier circuit 400and appears as a voltage value to an output of the column amplifiercircuit 400. Since the control signal psw_ref is set to the low levelfrom the high level, noises which are generated by the reference voltageconnecting switch 230 due to the charge injection or clock feed throughare amplified by the column amplifier circuit 410 and appear as avoltage value to an output of the column amplifier circuit 410. At thistime, since the control signal pgain<0> is at the low level and thecontrol signal pgain<1> is at the high level, feedback capacitances ofthe column amplifier circuits 400 and 410 are equal to Cf2 and the gainis determined by ratios between the capacitances Cf2 and Cr and Cref.

At this time, the noises generated by the color selecting switch 201 arecontained in the output voltage of the column amplifier circuit 400together with the color signal component of the R pixel 100. The noisesgenerated by the color selecting switch 201 are the noise componentcaused by the charge injection or clock feed through in a manner similarto the noises generated by the reference voltage connecting switch 230.Since the gains of the column amplifier circuits 400 and 410 coincide,the noises generated by the color selecting switch 201 appear to theoutput of the column amplifier circuit 400 as a magnitude that is almostequal to that of the noises which are generated by the reference voltageconnecting switch 230 and are contained in the output of the columnamplifier circuit 410. The column amplifier circuit 410 amplifies thereference voltage Vref at the same gain as that of the pixel signal ofeach color filter of the column amplifier circuit 400.

For a period of time from time t2 to t3, after the control pulse Φ2 wasset to the low level, when the control pulse Φ1 is set to the high leveland the horizontal scanning pulse phs<0> is set to the high level, thehorizontal read out switch 513 is turned on. Thus, the read-out of theoutput of the column amplifier circuit 410 is started and the signalbased on the reference voltage Vref from the column amplifier circuit410 is held in the clamping capacitor 610 (FIG. 3).

For a period of time from time t4 to t5, when the horizontal scanningpulse phs<1> is set to the high level, the horizontal read out switch503 is turned on. Thus, the color signal of the R pixel 100 from thecolumn amplifier circuit 400 is input to the difference detector 600. Adifference between the signal based on the reference voltage Vref andthe color signal of the R pixel 100 is output to the outside through thebuffer circuit 650 (FIG. 3). At this time, since the gains of the columnamplifier circuits 400 and 410 are equal, the noises generated by thereference voltage connecting switch 230 and the color selecting switch201 are contained in the signal based on the reference voltage Vref andthe color signal of the R pixel 100, respectively. Those noises have acorrelation between the circuit constructions after the color selectingswitch 201 and the reference voltage connecting switch 230 and theiroperations. By executing the difference process by the differencedetector 600, those noises are set off and reduced. Therefore, the colorsignal of the R pixel 100 in a state where the noises generated by thecolor selecting switch 201 were reduced is output to an output terminalVout.

Subsequently, at time t5, the read-out of the color signal of the Rpixel 100 is finished and a read out process of the color signal of theG pixel 110 is started. For a period of time from time t5 to t6, theoperation similar to the operation of the color signal of the R pixel100 which is executed for the period of time from time t1 to t2 isapplied to the G pixel 110 except a point that the resetting operationsof the column amplifier circuits 400 and 410 by the control signalpsw_ref and pc0 r are added. That is, the control signals psw_g andpsw_ref are set to the high level, the color selecting switch 202 andthe reference voltage connecting switch 230 are turned on, and the colorsignal of the G pixel 110 is input to the color signal input capacitor302. Since the color signal pgain<0> is set to the high level and thecolor signal pgain<1> is set to the low level at time t5, the gains ofthe column amplifier circuits 400 and 410 are determined by the ratiosbetween the capacitances Cf1 and Cg and Cref.

Since Cf1>Cf2 and the feedback capacitances increased, the gain of thecolor signal of the G pixel 110 is lower than that of the color signalof the R pixel 100. Thus, the noises which are generated by the colorselecting switch 202 and the reference voltage connecting switch 230 andappear in the outputs of the column amplifier circuits 400 and 410 aresmaller than the noises which are generated at the time of read out ofthe R pixel 100.

For a period of time from time t6 to t7, the operation similar to theoperation which was executed to the color signal of the R pixel 100 forthe period of time from time t2 to t5 is also executed to the colorsignal of the G pixel 110. At this time, the signal based on thereference voltage Vref and the color signal of the G pixel 110 which areused in the clamping process are the signals which were read out at thesame gain. Therefore, the noises which were generated by the referencevoltage connecting switch 230 and are contained in the signal based onthe reference voltage Vref have a magnitude similar to that of thenoises which were generated by the color selecting switch 202 and arecontained in the color signal of the G pixel 110.

Therefore, by executing the difference process by the differencedetector 600, the noises generated by the color selecting switch 202 canbe reduced. Thus, a difference between the color signal of the R pixel100 in a dark state and the color signal of the G pixel 110 decreases.

Subsequently, the operation similar to the operation which was executedto the color signal of the G pixel 110 for the period of time from timet5 to t6 is also executed to the color signal of the B pixel 120 for theperiod of time from time t7 to t8. That is, the control signals psw_band psw_ref are set to the high level, the color selecting switch 203and the reference voltage connecting switch 230 are turned on, and thecolor signal of the B pixel 120 is input to the color signal inputcapacitor 303. At this time, when both of the control signals pgain<0>and pgain<1> are set to the high level at time t7, the feedbackcapacitances of the column amplifier circuits 400 and 410 are equal to(cf1+cf2). Since the feedback capacitances increase more than those atthe time of read out of the color signals of the R pixel 100 and the Gpixel 110, the gains of the column amplifier circuits 400 and 410decrease. Thus, the noises which are generated by the color selectingswitch 203 and the reference voltage connecting switch 230 and appear inthe outputs of the column amplifier circuits 400 and 410 with respect tothe B pixel 120 are smaller than the noises which are generated at thetime of the R pixel 100 and the G pixel 110.

For a period of time from time t8 to t9, the operation similar to theoperation which was executed to the color signal of the G pixel 110 forthe period of time from time t6 to t7 is also executed to the colorsignal of the B pixel 120. At this time, the signal based on thereference voltage Vref and the color signal of the B pixel 120 which areused in the clamping process are the signals which were read out at thesame gain. Therefore, the noises which were generated by the referencevoltage connecting switch 230 and are contained in the signal based onthe reference voltage Vref have a magnitude similar to that of thenoises which were generated by the color selecting switch 203 and arecontained in the color signal of the B pixel 120.

Therefore, by executing the difference process by the differencedetector 600, the noises generated by the color selecting switch 203 canbe reduced. Thus, a difference between the color signal of the B pixel120 in the dark state and the color signal of the G pixel 110 and adifference between the color signal of the B pixel 120 in the dark stateand the color signal of the G pixel 110 decrease.

The read out of the signals is completed at time t9. At this time, it isassumed that a period of time from time t2 to t9 is set to onehorizontal scanning period and charge accumulation periods of the colorsignals of the R pixel 100, G pixel 110, and B pixel 120 which areoutput from the output terminal Vout for one horizontal scanning periodcoincide.

The color signals of the coincident gain of the column amplifiercircuits 400 and 410 and the reference voltage Vref are output duringthe same horizontal scanning period and differences between the colorsignals of the coincident gain and the signal based on the referencevoltage Vref are obtained by the difference detector 600. Therefore, thenoises which are generated by the reference voltage connecting switchgroup 200 can be reduced. Thus, a difference between the signal levelsdue to the colors which are typically seen because the gains of thecolumn amplifier circuits 400 and 410 differ every color irrespective ofthe dark state can be reduced. When the dark signal is obtained,characteristics in which the DSNU was decreased can be obtained.

The invention has been described above with respect to the embodiment inwhich the pixels of each color are constructed by one pixel. Timing inthe case of reading out a plurality of line-shaped pixel signals will besimply described hereinbelow. In FIG. 2, with respect to the signalamplified by the amplifier 402, the horizontal scanning pulses phs<1> isset to the high level for the period of time from time t4 to t5 as forthe signal of the R pixel 100, it is set to the high level for theperiod of time before time t7 as for the signal of the G pixel 110, andit is set to the high level for the period of time before time t9 as forthe signal of the B pixel 120. Therefore, the horizontal read out switch503 is turned on and the signals are sequentially output to thehorizontal common output line 701. If the difference process is executedby using the signal based on the common reference voltage Vref to aplurality of same color signals, since it is sufficient to read out thereference voltage Vref once to the line-shaped pixel signals, a read outtime can be shortened. Or, the reference voltage Vref may be read outevery pixel signal or every plural signals.

Although the embodiment has been described with respect to the casewhere the pixels of the three colors of R, G, and B were applied, theinvention is not limited to such a case. For example, a monochromaticpixel without a color filter may be provided in addition to the pixelsof the three colors of R, G, and B. This is true of the followingembodiments.

Although the embodiment has been described with respect to such acircuit construction that the gains of the column amplifier circuits 400and 410 of the color signal and the reference voltage Vref are equal,the invention is not limited to such a case. It is also possible to usesuch a circuit construction and setting that the gains of the columnamplifier circuits 400 and 410 of the color signal and the referencevoltage Vref are close to each other to such an extent that the DSNUperformance which is required can be satisfied. At this time, it isassumed that magnitude relations between the gains of the columnamplifier circuits 400 and 410 of the color signal and the referencevoltage Vref coincide. For example, when the gain of the R pixel 100 islarger than the gains of the G pixel 110 and the B pixel 120, thefollowing processes are executed. That is, it is assumed that the gainof the reference voltage Vref in which the CDS (correlation doublesampling) process is executed to the color signal of the R pixel 100 isalso larger than the gain of each reference voltage Vref in which theCDS process is executed to the color signals of the G pixel 110 and theB pixel 120. Therefore, if the gain of the reference voltage Vref cansatisfy the DSNU performance, it is not always necessary that it isequal to the gain of the R pixel 100. This is true of the followingembodiments.

Although the noises which are generated by the color selecting switches201 to 203 have been reduced by using the reference voltage Vref in theembodiment, the invention is not limited to such a case. For example, anoutput signal from an OB pixel (optical black pixel) in which aphotosensing portion has been shielded against the light by a metallayer or the like may be used as a reference voltage Vref or a resetpotential of the pixel may be used as a reference voltage Vref. That is,the reference voltage Vref may be produced by the light-shielded opticalblack pixel.

The difference detector 600 in the embodiment is not limited to thecircuit construction illustrated in FIG. 3 but, for example, a circuitconstruction as illustrated in FIG. 4 may be used. The differencedetector 600 in FIG. 4 is constructed by: a reference voltage holdingcapacitor 680 to hold the reference voltage; a reference voltage S/Hswitch 660 for controlling the sampling to the reference voltage holdingcapacitor 680; and a differential amplifier 690. The timing chart ofFIG. 2 can be applied to the difference detector 600 in FIG. 4. Even ifthe difference detector 600 is provided in the outside of a chip, theeffect by the embodiment can be similarly obtained.

Second Embodiment

FIG. 5 is a diagram illustrating an example of a construction of aphotoelectric conversion apparatus according to the second embodiment ofthe invention. FIG. 6 is a timing chart illustrating an example ofprocesses of the photoelectric conversion apparatus of FIG. 5. Accordingto the embodiment, a variation in offset voltage between the amplifiersat the time when the column amplifier circuits 400 and 410 areinitialized is reduced. The second embodiment will now be describedhereinbelow with respect to a point different from the first embodiment.

A circuit in FIG. 5 will now be described with respect to a pointdifferent from the circuit in FIG. 1. In FIG. 5, the output signals ofthe column amplifier circuits 400 and 410 are held in line memories 500and 510 until the horizontal scanning period. Color signalsampling/holding control switches 501 and 511 are controlled by acontrol pulse pts. Second capacitors 502 and 512 are color signalsampling capacitors for holding the color signals amplified by thecolumn amplifier circuits 400 and 410 and the signal based on thereference voltage Vref. The second capacitors 502 and 512 in the linememories 500 and 510 are the capacitors for holding the color signalsamplified by the column amplifier circuits 400 and 410 and the referencevoltage. Hereinbelow, the capacitors 502 and 512 are assumed to be Ctsand Cts′. Offset voltage sampling/holding control switches 504 and 514are controlled by a control pulse ptn. First capacitors 505 and 515 areoffset voltage sampling capacitors for holding the offset voltages ofthe column amplifier circuits 400 and 410. The first capacitor 505 inthe line memory 500 is a capacitor to hold the offset voltage at thetime of initialization of the column amplifier circuit 400. Hereinbelow,the capacitor 505 is assumed to be Ctn. Horizontal read out switches 506and 516 are controlled by the horizontal scanning pulses phs<0> andphs<1> and are provided to transmit the offset voltage held in thecapacitor Ctn to a horizontal common output line 702. The horizontalread out switches (506 and 503) and (513 and 516) are used to read outthe offset voltage held in the first capacitor Ctn and the pixel signalheld in the second capacitor Cts to the different horizontal commonoutput lines 702 and 701 by the horizontal scanning pulses phs<0> andphs<1>, respectively. Horizontal common output line resetting switches703 and 704 are controlled by a control pulse pchr and are provided toreset the horizontal common output lines 701 and 702 to a reset voltageVchr.

The timing chart of FIG. 6 will be described hereinbelow with respect toa point different from the timing chart of FIG. 2. In FIG. 6, as shownin a period of time from time t2 to t3, when the control pulses ptn andpts are set to the high level, the switches 504 and 501 are turned on.Thus, the color signal of the R pixel 100 and the signal based on thereference voltage Vref as output signals from the column amplifiercircuits 400 and 410 are temporarily held in the capacitors 505 and 502.After that, for a period of time from time t4 to t7, when the horizontalscanning pulses phs<0> and phs<1> are set to the high level, thehorizontal read out switches 503 and 506 are turned on and the signalsheld in the capacitors 502 and 505 are sequentially transmitted to thehorizontal common output lines 701 and 702. At this time, in a mannersimilar to the first embodiment, by obtaining a difference between thesignal components held in the capacitors Cts and Ctn of the linememories 500 and 510 which are simultaneously output, the offset-basednoises which are generated by the column amplifier circuits 400 and 410can be reduced. The color signals of the G pixel 110 and the B pixel 120are also read out by the operation similar to that for the R pixel 100.

Although the embodiment has been described with respect to theconstruction in which the difference process between the signal based onthe reference voltage Vref and each color signal is executed in theoutside of the chip, it is also possible to use such a construction thata circuit for executing the difference process like a process that isexecuted in the difference detector 600 in FIG. 1 as mentioned above isbuilt in the chip.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2012-118870, filed on May 24, 2012, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A photoelectric conversion apparatus comprising:a plurality of pixels having mutually different color filters, andgenerating pixel signals by a photoelectric conversion; a colorselecting switch configured to select the pixel signals generated by theplurality of pixels having mutually different color filters; a firstamplifier circuit configured to amplify at mutually different gains thepixel signals generated by the pixels having mutually different colorfilters and selected by the color selecting switch; a reference voltageconnecting switch configured to select a reference voltage; and a secondamplifier circuit configured to amplify at mutually different gains thereference voltages correspondingly to the pixel signals of mutuallydifferent colors.
 2. The photoelectric conversion apparatus according toclaim 1, wherein the second amplifier circuit amplifies the referencevoltages, at the same gains of the first amplifier circuit in amplifyingthe pixel signals of corresponding colors.
 3. The photoelectricconversion apparatus according to claim 1, further comprising adifference detector configured to perform a difference processingbetween the pixel signal amplified by the first amplifier circuit andthe reference signal amplified by the second amplifier circuit.
 4. Thephotoelectric conversion apparatus according to claim 2, furthercomprising a difference detector configured to perform a differenceprocessing between the pixel signal amplified by the first amplifiercircuit and the reference signal amplified by the second amplifiercircuit.
 5. The photoelectric conversion apparatus according to claim 1,further comprising a read out switch configured to read out in a timedivision to the same output line the pixel signal amplified by the firstamplifier circuit and the reference signal amplified by the secondamplifier circuit.
 6. The photoelectric conversion apparatus accordingto claim 4, further comprising a read out switch configured to read outin a time division to the same output line the pixel signal amplified bythe first amplifier circuit and the reference signal amplified by thesecond amplifier circuit.
 7. The photoelectric conversion apparatusaccording to claim 1, further comprising a first capacitor configured tohold an offset voltage at an initializing the first amplifier circuit,and a second capacitor configured to hold the pixel signal amplified bythe first amplifier circuit.
 8. The photoelectric conversion apparatusaccording to claim 7, further comprising a read out switch configured toread out, to the different output lines, the offset voltage held by thefirst capacitor, and the pixel signal held by the second capacitor. 9.The photoelectric conversion apparatus according to claim 1, wherein thereference voltages is generated by an optical black pixel shielded fromlight.